Forces are needed to cause objects to move or stop. Moving objects requires an unbalanced force acting on it, while balanced forces will not cause motion. There are two main types of forces that can cause motion - pushing forces and pulling forces. Examples include a person pushing a car or pulling a suitcase. Engineers have also harnessed the power of air forces to move objects like carts by using fire extinguishers. Motion refers to a change in an object's position relative to a fixed point, and can be easy to see like walking or more difficult to detect like leaves moving in the wind.

1. Session Thirteen

2. Do you think about how each of the objects start to move?
- The objects above requires a force to stop or move. This Force could be a pushing force or a pulling Force
- To move a stopped object the forces acting on it need to change
- we need energy to apply these forces to the objects where:
* The person in picture one needs energy to push the car
* The person in picture two needs energy to pull the suitcase
* The football player and picture 3 needs energy to push the ball while the goalkeeper needs energy to push
against the ball to stop it

3. Truck vs jet airplane:
- The engines on a jet airplane are much more powerful than the engines in a truck so jet airplane is flies much
faster than moving trucks
The shockwave truck:
- The truck in the opposite figure is known as the shockwave truck which has been fitted with 3 jet engines
How does this truck move? How does this truck stop?
The three jet engines make the
shockwave truck reach speeds more than
500 kilometers per hour which is about
five times faster than the normal
trucks
To stop this truck engineers turned to
the idea that is used in the rocket
designs where they installed three
parachutes that the driver opens to
help slow down the truck quickly

4. ©Salma Mostafa

5. All objects around us cannot move without push and pull forces where:
A ball lying on the ground doesn't
move until someone pushes it
with his foot to make the ball roll
A closed drawer doesn't open until
someone pulls the handle with his
hand to open the drawer
Air force:
-Air can provide enough Force to move some objects such as:
The wind blowing that can move the leaves of a tree
let's see how engineers prove that the force of air can move some objects like a “cart”

6. Cart activity:
- some engineers fix fire extinguishers onto a cart
- when they release air from the fire extinguishers, the
air moves backward that makes the cart begins to move
forward.
- by increasing the number of fire extinguishers, the speed
of the car increases and the distance that it moves
increases too and vice versa
Pushing force Pulling force
Example:
A man pushes
a wheelbarrow
Example:
A child pulls
a toy car
How do objects move?
There are two forces that causes objects to move which are:

7. ©Salma Mostafa

8. Balanced forces Unbalanced forces
If there are balanced forces act on an object so this
object will not move.
Example:
-In the tug-of-War game, if the two teams are
pulling the Rope with equal forces.
- This means that the forces that act on the Rope
are balanced (equal) forces
-so, this rope will not move
If there are unbalanced forces act on an object, so
this object will move.
Example:
-In the tug-of-war game, if one team is pulling the
rope with a greater force.
- This means that, the forces that act on the rope
are unbalanced (unequal) forces
-So, the rope will move towards the team with the
greater force
The relation between motion with balanced and unbalanced forces:

9. How do we know an object is moving?
- an object is moving if its position changes from one place to another, even if this change can’t be seen.
- the changing the position of an object is compared to something else that's not usually moving (fixed point)
It’s any change in the position of an
object relative to a fixed starting point
Motion:

10. ©Salma Mostafa

11. 1- The boy holding a ball in starting position
which is close to the tree
Examples on motion:
2- when he throws the ball, it will move by the
pushing force through the air
3- The ball will drop into the hands of the girl
by the pulling force of gravity
4- The ball will stop by the pushing force of the
girl’s hand against the ball movement
4- The position of the ball changes, relative to
the tree which is the fixed starting point

12. Some motions are easy to see, such as:
Some motions are Hard to see, such as:
A person
walking
down the
street
Leaves
move by
the wind
blowing
The rotation
of Earth
around the
sun